1. Field of the Invention
This invention relates to intravascular catheters suitable for delivering a radiation source to a body lumen for example of the kind used in the prevention of restenosis after arterial intervention.
2. Description of the Related Art
In a typical percutaneous transluminal coronary angioplasty (PTCA), for compressing lesion plaque against the artery wall to dilate the artery lumen, a guiding catheter is percutaneously introduced into the cardiovascular system of a patient through the brachial or femoral arteries and advanced through the vasculature until the distal end is in the ostium. A dilatation catheter having a balloon on the distal end is introduced through the catheter. The catheter is first advanced into the patient's coronary vasculature until the dilatation balloon is properly positioned across the lesion.
Once in position across the lesion, a flexible, expandable, preformed balloon is inflated to a predetermined size at relatively high pressures to radially compress the atherosclerotic plaque of the lesion against the inside of the artery wall and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile, so that the dilatation catheter can be withdrawn from the patient's vasculature and blood flow resumed through the dilated artery. While this procedure is typical, it is not the only method used in angioplasty.
In angioplasty procedures of the kind referenced above, restenosis of the artery often develops which may require another angioplasty procedure, a surgical bypass operation, or some method of repairing or strengthening the area. To reduce the likelihood of the development of restenosis and strengthen the area, a physician can implant an intravascular prosthesis, typically called a stent, for maintaining vascular patency. A stent is a device used to hold tissue in place or to provide a support for a vessel to hold it open so that blood flows freely. Statistical data suggests that with certain stent designs, the restenosis rate is significantly less than the overall restenosis rate for non-stented arteries receiving a PTCA procedure.
A variety of devices are known in the art for use as stents, including expandable tubular members, in a variety of patterns, that are able to be crimped onto a balloon catheter, and expanded after being positioned intraluminally on the balloon catheter, and that retain their expanded form. Typically, the stent is loaded and crimped onto the balloon portion of the catheter, and advanced to a location inside the artery at the lesion. The stent is then expanded to a larger diameter, by the balloon portion of the catheter, to implant the stent in the artery at the lesion. Typical stents and stent delivery systems are more fully disclosed in U.S. Pat. No. 5,514,154 (Lau et al.), U.S. Pat. No. 5,507,768 (Lau et al.), and U.S. Pat. No. 5,569,295 (Lam et al.), which are incorporated herein by reference.
Stents are commonly designed for long-term implantation within the body lumen. Some stents are designed for non-permanent implantation within the body lumen. By way of example, several stent devices and methods can be found in commonly assigned and common owned U.S. Pat. No. 5,002,560 (Machold et al.), U.S. Pat. No. 5,180,368 (Garrison), and U.S. Pat. No. 5,263,963 (Garrison et al.), which are incorporated in herein by reference.
Procedures for the prevention of restenosis after arterial intervention also have employed delivery of a radiation source through the arterial system to the area of the body lumen where the development of restenosis might occur. The radiation source may be delivered by an implanted stent containing a radioactive isotope in the metal which has a short half-life, or a wire having a radioactive source at the distal end that is temporarily placed in the arterial lumen.
However, a compromise had to be made between the shelf life of such radioactive implants and the in vivo efficacious lifetime of the device. If materials with short half lives were used in order to reduce long term radiation exposure of the patient, then the shelf life of the device was unacceptable. If an isotope was used with a long shelf life, then exposure of the patient to radiation was long term.
Radiation treatments using a radioactive wire placed in the artery lumen or inside a catheter were subject to a problem of maintaining a uniform dosage. Since this radioactive wire device is small relative to the artery lumen, the potential exists for it to rest in an off-center position. In this situation, locally high radiation burns were possible on one side of the arterial wall while the other side received a suboptimum dose.
Some radioisotopes considered for use in radiation delivery devices required ion implantation into the device or transmutation of the metal in the device, which would require extra handling and shielding of the device along with the increased cost and complexity of processes like transmutation.